The caged Garcinia xanthones have unique structures, potent bioactivities and largely unexplored biological mode of action. Recent findings from several laboratories, including our own, have shown that these molecules induce apoptosis in several cancer cells including multidrug resistant clones and have a good therapeutic window for potential applications in drug discovery. The mode of action of these compounds is proposed to involve binding to the transferrin receptor (TfR) but the binding site and consequences of this binding in cell signaling have not been examined. Here we present an interdisciplinary research program that would address issues related to the chemical biology of the caged Garcinia xanthones. We propose to determine the crystal structure of these molecules in complex with the human TfR ectodomain and identify their binding site. This information will be used to identify and optimize their pharmacophoric motif. We will measure binding constants of these compounds to TfR and correlate them to their cytotoxicity values. We will also evaluate whether binding of the small molecules to TfR affects TfR endocytosis and determine signaling pathways that become activated leading to apoptosis. This work will produce new information for structure-based drug design targeting the transferrin receptor and generate fundamental knowledge on the structure of the transferrin receptor and its role in cell signaling and apoptosis. PUBLIC HEALTH RELEVANCE: Extracts from the Garcinia family of tropical trees have yielded natural products with unique structure and promising biological activity. Our group has developed a chemical strategy to produce these compounds that not only eliminates problems associated with natural supply but also provides an opportunity to design a wide variety of related molecules with enhanced bioactivity. Through a collaborative effort we have found that several synthetic analogues have impressive bioactivities and induce selective killing of certain cancer cells including those that are resistant to current chemotherapy treatments. Here we propose to study in detail the actions of these compounds and determine how they kill cancer cells. Results from this investigation will produce new information on the cellular biology of cancer and will also lead to the development of new and effective anticancer drugs. As such, this research will have a significant impact to public health.